1. Field of the Invention
The present invention relates to an ink jet recording head and an ink jet recording apparatus using the ink jet recording head for performing the recording operation by discharging a recording liquid onto the recording surface of a recording medium.
2. Related Background Art
In an ink jet recording head, an electrothermal energy conversion element arranged in a recording liquid chamber is heated by being supplied with an electrical pulse as a recording signal thereby to impart thermal energy to the ink. Utilizing the bubble pressure generated by the bubbling (boiling) of the recording liquid due to the phase change of the recording liquid, minute ink droplets are discharged from at least a minute discharge port thereby to perform the recording operation on a recording medium.
The electrothermal energy conversion element of this ink jet recording head is heated and the interior of the recording liquid chamber is exposed to a high temperature. Desirably, therefore, the ink having the properties thereof not changed at a high temperature is selected while at the same time covering the various elements on the substrate with a protective film to protect the electric circuit elements from thermal damage. Also, the metal surface is liable to be corroded by a water hammer when the heated bubbles are extinguished, and therefore it is desirable to provide a protective film (anti-cavitation film).
In the conventional ink jet recording head, at least an electrothermal energy conversion element and at least an electrical circuit element are mounted on a substrate, and a protective film is formed on the assembly to give a heat resistance. The resulting assembly is formed with an anti-cavitation film over the entire surface thereof, followed by forming a discharge port forming member thereon. The discharge port forming member includes a flow path wall for defining a flow path in accordance with each electrothermal energy conversion element and a discharge port communicating with an external unit from the flow path and adapted to discharge the ink. This configuration exhibits the effect of protecting the electrothermal energy conversion element and the electrical circuit element. Nevertheless, the following problem is posed.
Firstly, the ill compatibility between a tantalum (Ta) film generally used as an anti-cavitation film and the discharge port forming member made of a synthetic resin causes the problem of a low adhesion. A low adhesion between the substrate and the discharge port forming member gives rise to a solution leakage from the flow path and the displacement of the discharge port, thereby sometimes making it impossible to perform the desired recording operation.
Secondly, an inspection pad is required to check the insulation between the protective film formed under the anti-cavitation film and the electrothermal energy conversion element and the electrical circuit element, thereby undesirably increasing the size of the substrate.
In order to solve the two problems described above, Japanese Patent Application Laid-Open No. 2002-79672 discloses a recording head comprising a first metal film as an anti-cavitation film covering the upper part of a recording element and a second metal film as an anti-cavitation film covering the upper part of an electrical circuit element, where the first and second metal films are provided in the shape of a pair of combs and are arranged in opposed relation with each other. This recording head can improve the adhesion between the substrate and the discharge port forming member due to a reduced ratio which the anti-cavitation film represents of the substrate. Further, the provision of an inspection pad on each of the first and second metal films described above makes it possible to inspect the protective film for a defect without increasing the substrate size.
However, the recording head disclosed in the patent publication described above comprises an inspection electrode pad for each of the first and second metal films, with the result that the substrate size is increased proportionately. To reduce the size of the substrate, therefore, the arrangement of the inspection pad is required to be more optimized.